Electromechanical bicycle gear shift mechanism

ABSTRACT

A bicycle gear shift mechanism (8) to be actuated by an electric motor (m) has a carrier for an actuator member (S) comprising a tensioning arm (29) of a derailleur or a shift plunger of a hub gear transmission. According to the invention, the carrier comprises a cursor (27) slidably displaceable on at least two spaced parallel guides (26) mounted at stationary positions with respect to a housing (18). According to a further aspect, a control circuit for the bicycle gear shift mechanism to be actuated by a DC motor comprises a first and a second power control circuit (70,71) controlled by first and second flip-flop circuits (60, 61) the set inputs of which are connected to switches (68, 69) for shifting to higher or lower gear ratios, and the reset inputs of which are adapted to by activated via a switch (65) which is responsive to the gear-engaged state of the gear shift mechanism.

DESCRIPTION

The invention relates to an electromechanical bicycle gear shiftmechanism of the type defined in the generic clause of patent claim 1.

Described in U.S. Pat. No. 39 19 891 is an embodiment of anelectromechanical gear shift mechanism of this type, in which one end ofa telescopically extensible three-sided housing is secured to thevehicle frame, the other end being operatively connected to an actuatormember by a pin. Mounted within the housing is a drive member in theform of a threaded spindle driven by an electric motor for retractingand extending the outer housing portion relative to the fixed housingportion in a direction parallel to the wheel axis. In an actuatingmechanism of this type the distance between the actuator member and thewheel axis remains constant, in contrast to the customary cinematics ofknown derailleur gear shift mechanisms employing a parallelogramlinkage, in which the shift actuator member is moved parallel to itselfand in addition along an arcuate path. In the case of this gear shiftmechanism known from U.S. Pat. No. 39 19 891 it is difficult toaccurately engage the individual gears with the chain correctlypositioned on the respective sprocket, because the reaction forces ofthe chain, travel-induced shocks and vibrations, and the gear shiftforces result in excessive loads acting on the relatively movablehousing portions, resulting in rapid wear and thus impairing the gearshift accuracy.

In a further electromechanical bicycle gear shift mechanism of anothertype known from U.S. Pat. No. 40 41 788, an electric motor is operableto move a lever arm carrying a floating gear adapted to assume twoengagement positions with respect to a spindle drive mechanism formoving a shift actuator member in opposite directions along an axisextending parallel to the rear wheel axis. The rotation of the spindledrive mechanism is derived from the chain movement. Associated to thechain tensioning lever and to the lever arm carrying the floating gearare a plurality of positioning wiper contacts included in the electricalcircuit for controlling the electric motor and serving for accuratelypositioning the shift actuator member in respective gear engagementpositions by reversing the electric motor controlling the gear shiftoperation when the tensioning lever reaches the accurate gear engagementposition to thereby disengage the floating gear at an accurately timedinstant.

Known from FR Patents 10 03 373 and 12 77 691 are purely mechanicalbicycle gear shift mechanisms in which the carrier of the shift actuatormember formed as a chain tensioning lever or a deflector sprocket isguided in a housing in a simple sliding guide assembly, any rotation ofthe carrier being prevented by a guide pin engaging a longitudinalgroove or by a non-circular cross-section of the carrier.

In an electromechanical bicycle gear shift mechanism known from FR-PS 2233 220, the carrier simultaneously acts as the shift actuator memberfreely guided in a transverse guide slot and threadedly engaged with aspindle connected to an electric motor. The electric control circuit ofthe motor contains series-connected reed switches and simple change-overswitches with control relais and diodes.

In an electromechanical bicycle gear shift mechanism known from FR-PS 2587 079, the embodiment comprising a shift actuator member displaceableparallel to the wheel axis, the actuator member is inadequately guidedon an exposed transverse guide bar. The control circuit for the electricmotor comprises printed circuit components and a plurality of wipercontacts highly sensitive to wear and contamination.

From GB-PS 004 05 09 there is finally known a linear motor of thestepped-motion type in which the position of the movable motor componentis monitored by an electro-optical sensing device comprising fotocells,receiving elements and a longitudinally extending scale and operating togenerate countable signals indicative of the position of the movablemotor component.

It is an object of the invention to provide an electromechanical bicyclegear shift mechanism of the type defined in the introduction, whichoffers a high degree of shifting accuracy and is resistant to wear overlong periods of use.

The cursor is safely protected within the housing and accurately guidedover its full admissible range of movement. The reaction forces of thechain, travel-induced shocks and vibrations, and gear-shifting forcesare thus transmitted from the cursor to the housing over a large area.The cursor is easily movable under the forces acting thereon. Dirt andmoisture are prevented from entering the guide portion of the cursor. Inthis manner a wear-reduced shifting operation with a high degree ofaccuracy and accurately reproducible shift movements is ensured over along time of use even in the case of frequent shifting operations.

In an advantageous embodiment the projection forms an extension of thecursor and projects from the housing through the slide seal gasket. Thisprovides effective protection against the entering of dirt and moistureat this location. The slide seal gasket may contribute to the guiding ofthe cursor, although this is not indispensable for proper operation.

In view of the fact that bicycle gear shift mechanisms are subjected tohigh demands regarding low maintenance and perfect reliability, and thatcompact dimensions are desirable, because the gear shift mechanismprojects beyond the contours of the bicycle in any case,, all of themovable elements are suitably combined and encapsulated in the smallestpossible space. This results in minimum dimensions.

A further advantageous embodiment comprises a construction in which thecursor cooperates effortless with its guides, and in which the slidingresistance to the cursor movements remains constant practicallyindependent of the influences of time and temperatures Even after a longtime of use, the shifting accuracy will not be impaired by theoccurrence of play between the cursor and its guides The cursor can bemanufactured at relatively low expenditure and with accurate dimensions,for instance on a mass-production base. The oval cross-sectional shaperesults in high dimensional stability and ensures a wide spacing of theguides, favouring accurate guidance even under relatively great forces.The oval cross-sectional shape also substantially conforms to that ofthe housing, so that the latter is given a pleasing appearance withcompact dimensions. The slide bearings merely have to be press-fittedinto the bores.

According to a further embodiment, the forces for the shifting movementsare introduced into the rack closely adjacent the guides, so thatharmful torque loads are substantially avoided. The positioning of therack on top and of the longitudinally extanding positioning element atthe bottom side of the cursor favours the compact dimensions desired forthe housing

In another advantageous embodiment the derailleur comprises a tensioningarm carrying two idler sprockets for the chain, mounted on a bearingstud secured to the carrier, and spring-biased in one direction ofrotation thereabout. The thus constructed mounting of the derailleur canbe readily accommodated in the cursor, resulting in the advantages ofcompact dimensions and a compact and stable retention of the tensioningarm. Practically the full length of the cursor and its extension isavailable for mounting the derailleur, so that there need not be anyexposed elements between the cursor and the derailleur. The housing ofthe gear shift mechanism may be placed closely adjacent the chain, sothat the distance it projects beyond the contours of the bicycle isminimized, to thereby reduce the dangers of injury or of damage to thehouses to a minimum.

In a structurally simple and readily mountable embodiment, thetensioning lever is not only capable of performing its proper movementsrequired for the tensioning function, but is also coupled to the cursorpractically without any play, so that the shifting movements areaccurately transmitted to the chain. This ensures that the shiftingaccuracy obtained by the reliable guidance of the cursor is also adheredto by the tensioning arm.

In a gear shift mechanism known from U.S. Pat. No. 4,041,788, a row ofwiper contacts is disposed on one housing wall. Movement of thetensioning arm causes a contact finger carried thereby to travel overthe wiper contacts. The closing of any contact indicates that adetermined gear shift position has been reached by the tensioning arm,enabling the motor to actuate a shifting lever for a drive gear tothereby terminate the movement of the tensioning arm. This constructionsuffers from the shortcoming that the wiper contacts are prone to wearand corrosion, and that the construction and operating principleemployed with its multi-component mechanical feedback system does notalways ensure that the tensioning arm stops at the position accuratelycorresponding to the selected gear shift position. Even small deviationsfrom this position, however, result in distortion of the chain on therespective sprocket, and in a noticeable reduction of the efficiency ofthe gear shift mechanism.

In an electromechanical bicycle gear shift mechanism, in which thehousing contains positioning means for the carrier forming part of theelectric circuit for the control of the electric motor and aligned witha positioning element moving in unison with the carrier, it is anotherobject of the invention to simplify the construction for theaccommodation of the electric circuit and the cooperating positioningelements as far as possible and at the same time to ensure wear-free andreliable cooperation of the positioning components.

In an embodiment devised to attain this object, the circuit carrierplate can be readily incorporated in the housing without requiringadditional space therefor. The plate functions simultaneously as thecarrier of the positioning device. Since the positioning element isstructurally combined with the cursor acting as the carrier, the spacerequirements are reduced to result in compact dimensions. Thecontact-free cooperation between the positioning element and thepositioning device, and particularly the optoelectronic sensors, areeffective to avoid any wear. The indication of the actual position ofthe carrier is directly transmitted to the electric circuit. The sensorsare of a commercially available type, inexpensive, and capable oflong-time trouble-free operation thanks to their protected accommodationwithin the housing.

According to a further embodiment, the direction of rotation of theelectric motor is reversed to automatically return the gear shiftmechanism to the previously held gear shift limit position when the usererroneously enters a shifting pulse that would result in derailment ofthe chain because there is no further sprocket beyond the sprocketcorresponding to the gear shift limit position. In the case of the gearshift mechanism known from U.S. Pat. No. 40 41 788 it is not explainedby what means this problem is to be solved.

A further advantageous embodiment includes an inexpensive positioningelement capable of being easily manufactured and mounted. This elementdesirably contributes to the required shifting accuracy by permittingthe scanning ranges to be defined in a simple manner. The bifurcatelight barriers cooperate with the strip in a highly reliable manner.

Another advantageous embodiment provides the effect that in case oferroneous actuation surpassing the gear shift limit position, thedirection of rotation of the electric motor is reversed after thecarrier with the tensioning arm has moved by a small distance, tothereby return to the gear shift limit position, so that derailment ofthe chain is safely prevented. The limited movement of the carrier priorto the reversal of the electric motor results in a certain distortion ofthe chain with respect to the limit position sprocket, but only for avery short instance, so that the user is scarcely incommodated.

According to another embodiment the logic circuit component cooperateswith the sensor to prevent a shifting operation from being initiatedunless the movement of the chain is sufficient for ensuring a smooth andreliable shifting operation.

In another embodiment the stop reset feature is effective to ensure thatthe user is enabled to resume pedalling with a small or the smallesttransmission rate, without having to shift gears, after havingapproached a stop, for instance at a traffic light, with ) a greatertransmission rate. Otherwise it could by rather heavy work to start withthe previously selected great transmission rate.

From U.S. Patent there is also known a control circuit for anelectromechanical bicycle gear shift mechanism actuated by a DC motor.This known control circuit comprises a wiper contact disc connected tothe DC motor and rotatably mounted opposite a plurality of wipercontacts associated to individual gear shift positions. A Bowden cableoperatively connects the rotatable disc to a derailleur of the sameconstruction as the derailleur of a mechanically operable bicycle gearshift mechanism. Provided on the handlebar of the bicycle is a switchcontact set operable by means of a rotatable lever and electricallyconnected to the wiper contacts, so that the desired operation of the DCmotor is achieved in response to the position of the switch contacts andthe rotary position of the contact disc. Due to the great number ofelectromechanical components and wiper contacts, this known gear shiftmechanism is excessively expensive in production, and in additionscarcely suitable for operation under varying environmental conditionstypical in use of a bicycle gear shift mechanism.

It is therefore further intended to improve a control circuit for anelectromechanical bicycle gear shift mechanism operable by a DC motor,to thereby increase its reliability in operation which while achievingan extremely simple mechanical construction of the control circuit.

An embodiment of the invention shall now be described in detail withreference to the accompanying drawings, wherein:

FIG. 1 shows a bicycle having an electromechanical gear shift mechanism,

FIG. 2 shows a partially sectioned perspective view of theelectromechanical gear shift mechanism with components of the rear wheeldrive transmission system,

FIG. 3 shows a perspective view, partically in section, of an enlargeddetail of FIG. 2,

FIG. 4 shows an enlarged detail of FIG. 2,

FIG. 5 shows a control circuit for an electromechanical bicycle gearshift mechanism, particularly of the type described with reference toFIGS. 1 to 4,

FIG. 6 shows a detail of the control circuit of FIG. 5, and

FIG. 7 shows a further detail of the control circuit of FIG. 5.

A bicycle 1 has a frame 2 with a front wheel 3 and a rear wheel 4mounted in the conventional manner in a rear end portion 5 of frame 2.Rear wheel 4 is rotated from a pedal crank sprocket 6 via a chain 9 anda diagrammatically indicated sprocket stack 7 formed of a plurality ofchain sprockets defining respective gear shift stages with differenttransmission rates of the circumferential speed of the pedal cranksprocket. An electromechanical gear shift mechanism 8 indicated in FIG.1 merely diagrammatically is secured to rear frame end portion 5 forselecting the different gear shift stages. A current source 10 isprovided for supplying electric current to the gear shift mechanism, andoptionally to bicycle lighting fixtures (not shown). Gear shiftmechanism 8 may for instance be operated by means of a gear shiftselector 11 mounted on the handlebar. Associated to pedal crank sprocket6 is a conventional crank bearing dynamo 12 which may also be used as acurrent source.

Shown in FIG. 2 are details of gear shift mechanism 8 and sprocket stack7.

Secured to a rear wheel hub 13 is a splined drive transmission sleeve 14carrying a number of sprockets corresponding to the number of gear shiftstages. Shown in FIG. 2 is a sprocket 15a for the limit gear shift stagewith the smallest transmission ratio, and an adjacent sprocket 15b for agear shift stage with a greater transmission ratio. As the selectedtransmission ratios become greater, the number of revolutions of rearwheel 4 increases for each revolution of pedal crank sprocket 6.

A sidewall 16 of a closed housing 18 is also secured to rear end portion5 of frame 2 by means of a clamp screw 19 also serving for securing therear wheel, and a dowel pin 17. The position of sidewall 16 and thus ofhousing 18 relative to rear frame end portion 5 is finely adjustable bymeans of an adjustment screw 20.

Incorporated in housing 18 is a housing 21 of an electric motor Mincluding a reduction gear 22 and a drive pinion 23 in such a mannerthat the rear end of housing 21 projects from housing 18 and drivepinion 23 is positioned within housing 18. The longitudinal axis ofmotor M extends substantially perpendicular to the longitudinal axis ofhousing 18, i.e. substantially parallal to rear wheel 4. By contract,the longitudinal axis of housing 18 extends substantially parallel tothe rear wheel axis. Housing 18 has a circumferentially extendingenclosure wall 24 and a cover 25 secured to the side facing away frombicycle 1. Extending between sidewall 16 and cover 25 are parallelspaced rod-shaped guides 26 for a cursor 27 of oval cross-sectionalshape. Cursor 27 is of shorter length than the interior of housing 18(cf. also FIG. 3). It is integrally formed with a cylindrical extension28 extending through a slide seal 35 mounted in sidewall 16. A shiftactuator member S for engaging the selected gear shift stages is securedto cursor 27. In the embodiment shown, shift actuator member S is aso-called tensioning arm 29 carrying freely rotatable idler sprockets 30and 30a (cf. FIG. 3).

As evident from FIG. 2 in connection with FIG. 1, the lower run of chain9 extends from pedal crank sprocket 6 around idler sprocket 30 frombelow, around the other idler sprocket 30a, and rearwards around theselected sprocket 15a or 15b, and then again forwards to pedal cranksprocket 6.

Mounted in housing 18 as a housing bottom or on top of a not shownhousing bottom is a plate 31 carrying a likewise not shown controlcircuit for electric motor M and connected to gear shift selector 11 andalso to current source 10.

A longitudinally extending rack 32 is mounted on the top surface ofcursor 27 or formed integrally therewith to mesh with drive pinion 23.Secured to the bottom side of cursor 27 or formed integrally therewithis a positioning element 33, in the present embodiment a longitudinallyextending, upstanding strip or web (FIG. 4). A positioning deviceprovided for cooperation with positioning element 33 is shown in FIG. 2to comprise a bifurcate light barrier 34.

According to FIG. 3, cursor 27 is a pressure-casting or injection-moldedplastic member having an oval cross-sectional shape and integrallyformed with extension 28. Cursor 27 is formed with two bores 52extending parallel to its longitudinal axis, with linear antifrictionbearing 36 press-fitted therein, by means of which cursor 27 is guidedon rod-shaped guides 26. Between bores 52 cursor 27 is formed with alarger stepped bore 37 in which a bearing stud 38 of tensioning arm 29is rotatably mounted in a spring-biased state. A coiled spring 39envelops bearing stud 38 over part of its length. One end 40 of coiledspring 39 is anchored to a collar 43 of bearing stud 38, its other end42 being anchored in extension 28. Coiled spring 39 is tensioned to biastensioning arm 29 clockwise in FIG. 3, thus permitting the arm to yieldto forces acting counterclockwise clockwise thereon, but tending toautomatically return it in the opposite direction. Adjacent the frontend of extension 28 stepped bore 37 is provided with a friction bearing41 in which bearing stud 38 is mounted and which may be formed with anaxial bearing surface directed towards tensioning arm 29, so that thelatter is easily rotatable. From the other end of stepped bore 37 aretaining bolt 44 is screwed into bearing stud 38, the head 45 and partof the shank of retaining bolt 44 being rotatably received in a frictionbearing 46. The latter may also be provided with an axial bearingsurface 47 for head 45, so that the assembly formed of tensioning arm29, bearing stud 38 and retaining bolt 44 is easily rotatable in cursor27 without any axial play.

Shown in FIG. 4 is the manner in which plate 31, which carries thecontrol circuit shown in FIGS. 5 to 7, supports the positioning devicecomposed of bifurcate light barrier 34, another bifurcate light barrierm, and a third bifurcate light barrier 34a.

Bifurcate light barrier 34m is responsible for the individual possiblegear shift positions and for the respective correct positions of cursor27. Bifurcate light barriers 34 and 34a act as limit light barriers andare effective in the case of faulty actuation to prevent the cursor frombeing displaced to a position in which the chain would be derailed fromrespective end sprockets, for instance 15a.

Positioning element 33, which as already mentioned is an upright sheetmetal or plastic strip, is secured to the bottom side of cursor 27 andahs a plurality of scanning locations 48 formed in the present exampleas bores at spacings corresponding to those of the gear shift positions.Scanning locations 48a and 48b thus correspond to sprockets 15a and 15bshown in FIG. 2. Positioning element 33 further has front and rearscanning edges 49 and 50, respectively, for cooperation with limit lightbarriers 34 and 34a. The distance between light barrier 34m and each oflimit light barriers 34 and 34a exceeds the distance between a limitscanning location 48a and its associated scanning edge 49, of betweenthe other limit scanning location (indicated at 48 in FIG. 4) and theassociated scanning edge 50, respectively, by e length a.

The described electromechanical gear shift mechanism operates asfollows:

Assuming the the chain is engaged with sprocket 15a in the limit gearshift stage with the smallest transmission ratio, and the rider ispedalling, so that the chain is moving, a gear shift operation may beinitiated by a short actuation of the gear shift selector. This resultsin electric motor M being energized by the electric control circuit tothereby displace cursor 27 in the desired direction by the engagement ofpinion 23 with rack 32. This causes scanning location 48a to leavebifurcate light barrier 34m as cursor 27 moves to the right in FIG. 4(double arrow 51). The electric control circuit keeps electric motor Menergized until the next scanning location 48b is aligned with thepreviously interrupted light beam of bifurcate light barrier 34m. Atthis instant the electric control circuit operates to deenergizeelectric motor M and to stop it by electrical braking action. Theelectric control circuit is provided with a so-called pulse barrier, sothat it accepts a subsequent directional pulse only after a previous onehas been processed. During the described operation tensioning arm 29 hasshifted the chain from sprocket 15a onto sprocket 15b in an accuratelyaligned position.

If the rider has erroneously entered a directional pulse in the wrongdirection, involving the danger that tensioning arm 29 would derail thechain from sprocket 15a, the electric control circuit acts to energizeelectric motor M for displacement of cursor 27 to the left in FIG. 4. Inthis case, after displacement over the length a scanning edge 49interrupts the light beam of limit light barrier 34a, whereupon theelectric control circuit acts to reverse the rotation of electric motorM to return cursor 27 to the right in FIG. 4 to the position in whichscanning location 48a is again aligned with light barrier 34m, so thatthe gear shift mechanism is maintained in the previously held limitshift stage. The rider may then enter a shift pulse in the oppositedirection for causing the desired shifting operation to be properlyperformed.

It would also be conceivable to install electric motor M with its axisparallel to the longitudinal axis of housing 28, in which case thedisplacements of the cursor could be controlled by a worm drive orthreaded spindle mechanism.

Tensioning arm 29 might also be replaced by a gear shift plunger actingas a shifting actuator S for shifting the various shifting stages in ahub gear shift mechanism.

If the pedal crank assembly is provided with a plurality of sprockets ofdifferent size, a gear shift mechanism corresponding to gear shiftmechanism 8, but having a smaller number of shifting stages, could alsobe provided at this location.

A preferred embodiment of the control circuit according to the inventionshall now be described in detail with reference to FIG. 5. Controlcircuit 31 includes a first flip-flop circuit 60 and a second flip-flopcircuit 61. First flip-flop circuit 60 belongs to the upper section ofthe circuit shown in FIG. 5 for the up-shifting operation, while secondflip-flop circuit 61 belongs to the lower circuit section in FIG. 5 forthe down-shifting operation. Each flip-flop circuit 60, 61 has aninverting output Q and a non-inverting output Q, a set input S and areset input R. Connected to the inverting outputs Q of the respectiveflip-flop circuits 60, 61 via respective photo-transistors 66, 67 are afirst and a second power control circuit 70, 71 each composed of twooperation amplifiers 70a, 70b and 71a, 71b connected in series. At acommon input junction 74 each power control circuit 70, 71 is suppliedwith a reference voltage in the form of an intermediate voltage betweena first and a second voltage generated by a voltage divider 72, 73. Acommon circuit section 75 is provided for supplying power controlcircuits 70, 71 with a supply voltage. In addition, first power controlcircuit 70 is supplied with the second voltage, and second power controlcircuit, with the first voltage. When the input signal of first powercontrol circuit 70 is "high" and the input signal of second powercontrol circuit is "low", the output signal of first power controlcircuit 70 is substantially equal to the first voltage, while that ofsecond power control circuit 71 substantially equals the second voltage.When the input signal of first power control circuit 70 is "low" andthat of second power control circuit 71 is "high", the output signal offirst power control circuit 70 substantially corresponds to the secondvoltage, while that of second power control circuit 71 substantiallyequals the first voltage. The output signals of power control circuits70 and 71 are applied to DC motor M.

A phototransistor 65 in its activated state acts to connect the resetinputs of the two flip-flop circuits 60, 61 to the second voltage.Phototransistor 65 cooperates with a light emitting diode 62 to form thefirst bifurcate light barrier 34m already referred to in context withthe description of FIG. 4.

In the properly engaged state of the various gear shift stages of thebicycle gear shift mechanism, the light path between this (first) lightemitting diode 62 and the (first) phototransistor 65 extends through arespective scanning window 48a, 48b of positioning element 33. During agear shift operation positioning element 33 interupts the light path,causing first phototransistor to assume its nonconductive state.

The set input S of first flip-flop circuit 60 is connected to invertingoutput Q of second flip-flop circuit 61 through an UP switch 68. The setinput S of second flip-flop circuit 61 is connected to inverting outputQ of first flip-flop circuit 60 through a DOWN switch 69. The invertingoutput of first flip-flop circuit 60 is further connected to a shiftstop circuit 77 itself connected to a chain sensor 78 and a rotary speedsensor 79.

As shown in FIG. 6, chain sensor 78 comprises a magnetoelectric movementsensor 90, a pair of inversely connected diodes 91, a switchingamplifier 92 and an output diode 93 for sensing the movement of thechain.

Rotary speed sensor 79 is connected to a generator 80 acting to generatean AC output signal with an amplitude proportional to the bicycle speed.Rotary speed sensor 79 comprises a diode 94 and an RC circuit 95 to 97for converting this output to a DC voltage signal the amplitude of whichis indicative of the actual bicycle speed. When stop shift circuit 77senses a stationary condition of the bicycle on the basis of the outputsignals of chain sensor 78 and rotary speed sensor 79 applied thereto,it generates a "high" output signal which is applied to the set input ofsecond flip-flop circuit 61.

A second light emitting diode 63 and a third light emitting diode 64cooperate with second and third phototransistors 66, 67 to form thelimit light barriers 43 and 34a, the functions of which have alreadybeen explained with reference to FIG. 4. When positioning element 33assumes its respective end or limit positions, the light path fromsecond or third light emitting diode 63, 64 to second or thirdphototransistor 66, 67 is interrupted, causing the latter to assume itsnon-conductive state. This causes the associated one of power controlcircuits 70, 71 to be switched over, so that the polarity of the motorcontrol signal is reversed, causing the motor to reverse its directionof rotation until positioning element 33 has returned to the position inwhich a scanning location 48a, 48b is aligned in the light path betweenfirsz light emitting diode 62 and first phototransistor 65, whereuponflip-flop circuits 60, 61 are returned to their reset state.

The function of the hitherto described components of control circuit 31shall now be explained. Proceeding from an intermediate gear shiftstage, when UP switch 68 is actuated, a set signal is applied to firstflip-flop circuit 60. As a result, first power control circuit 70generates a "high" output signal, causing motor M to rotate in theselected direction. Even if Up switch 68 opens during this rotation ofmotor M and the corresponding displacement of positioning element 33between two gear shift positions, the described state of energization ismaintained until a reset signal is applied to the reset input of firstflip-flop circuit 60. This reset signal is generated when the respectivenext scanning window of positioning element 33 is aligned in the lightpath between first light emitting diode 62 and first phototransistor 65.This reset operation returns both flip-flop circuits 60, 61 to theirreset state, so that the output signals of both power control circuits70, 71 are "low", causing motor M to be stopped. A DOWN-shift operationis initiated by actuation of DOWN switch 69 and proceeds in a similarmanner as the UP-shift operation.

Any shifting operation beyond the high or low limit shift stages in thecase of erroneous actuation of switches 68 or 69 is prevented, asalready described, by the response of the phototransistors 66, 67 offirst or second limit light barriers 34 or 34a, causing the direction ofmovement to be reversed after the positioning element has reached itsrespective limit position.

When the rider of the bicycle comes to a stop with his bicycle in highgear, this condition is sensed by shift stop circuit 77 by means ofsensors 78 and 79. In response to this state, a "high" control signal isapplied to second flip-flop circuit 61, causing the gear shift mechanismto shift down to the lowest gear.

The control circuit is energized by a current source 10 to which aheadlamp 88 and a taillight 89 are additionally connected through alight switch 87.

Current source 10 includes generator 80 connected to an accumulator 82through a rectifier 81. Also connected to generator 80 is a timercircuit which is responsive to the generator output signal droppingbelow a minimum value or to zero volts for more than a predeterminedperiod of for instance two minutes. In this case an output switch 84 iscaused to open, so that any further current consumption by the controlcircuit and by the DC motor is avoided in the stationary condition ofthe bicycle. An enable switch circuit 85 likewise connected to generator80 responds to the output voltage of generator 80 rising above apredetermined minimum value of for instance one volt for actuating anassociated switch 86, to thereby achieve optimum charging and consumercharacteristics of the control circuit.

Generator 80 may be provided in the form of a pedal crank bearingdynamo.

The control circuit according to the invention may also be energized byan accumulator to be charged from a power mains outlet. In this casecurrent source 10 with generator 80 may be omitted.

A switch provided at the output side of generator 80 permits thegenerator or dynamo to be switched on and off at will. In this manner,the dynamo may be switched off when riding uphill, and activated forcharging accumulator 82 when coasting downhill.

The control circuit according to the invention Is not only suitable foremploy with the described bicycle gear shift mechanism, but may also beemployed with any other bicycle gear shift mechanism actuated by a DCmotor.

I claim:
 1. An electromechanical bicycle gear shift mechanism (8)comprising a housing (18) secured to a frame and carrying an electricmotor (M), a carrier for a shift actuator member (S) in the form of atensioning arm (29) of a derailleur or a shifting plunger of a hub geartransmission, said carrier being mounted in said housing forreciprocating displacement parallel to the wheel axis, a drivetransmission member adapted to be driven by the electric motor (M) andoperatively connected to said carrier, and an electric circuit for saidelectric motor (M) adapted to be controlled through a gear shiftselector (11), characterized in that said carrier is a cursor (27)slidably mounted in said housing (18) on at least two mutually spacedparallel guides (26) fixedly connected to said housing (18), the side ofsaid cursor (27) facing towards said shift actuator member (S) beingprovided with a preferably integrally formed extension (28) extendingthrough a sliding seal gasket (35) in a sidewall (16) of said housing(18) facing towards the wheel (4).
 2. An electromechanical bicycle gearshift mechanism according to claim 1, characterized in that said guides(26) comprise rods anchored between housing walls (16, 25), that saidcursor (27) is mounted on said guides (26) by means of sliding bearings(36), preferably linear anti-friction bearings, secured in respectivebores (52), and that said cursor (27) is a metallic pressure casting oran injection-molded plastic body of oval cross-sectional shape formedwith a through-bore (37) also passing through said extension (28) anddisposed between said bores (52) for said slide bearings (36).
 3. Anelectromechanical bicycle gear shift mechanism according to claim 1,characterized in that said electric motor (M) has a gear transmission(22) integrated in said housing (18) in such a manner that thelongitudinal axis of said electric motor (M) extends substantiallyhorizontal and perpendicular to the direction of movement of said cursor(27).
 4. An electromechanical bicycle gear shift mechanism according toclaim 1, characterized in that said drive transmission member is a rack(32) mounted on said cursor (27) and meshing with a drive pinion (23) ofsaid gear transmission (22).
 5. An electromechanical bicycle gear shiftmechanism according to claim 4, characterized in that said rack (32) isdisposed on and preferably formed integrally with a top surface of saidcursor (27), and that a longitudinally extending positioning element(33) is disposed on, and preferably also integrally formed with a bottomsurface of said cursor (27).
 6. An electromechanical bicycle gear shiftmechanism according to claim 1, wherein said shift actuator membercomprises a tensioning arm (29) provided with two idler sprockets (30,30a) for the chain (9) and mounted in a spring biased manner or saidcarrier by means of a bearing stud (38), characterized in that saidbearing stud (38) together with a tensioning spring (39) is mounted insaid through-bore (37) of said cursor (27) by means of rotary bearingmeans (41, 46) and a retaining bolt (44).
 7. An electromechanicalbicycle gear shift mechanism according to claim 6, characterized in thatsaid through-bore (37) of said cursor (27) is formed as a stepped borewith its diameter decreasing in the direction towards said wheel (4),that said bearing stud (38) is inserted into said through-bore (37) fromthe end thereof facing towards the bicycle and retained by the retainerbolt (44) threaded thereinto from the opposite end, .that saidtensioning spring (39) is a coiled spring having one end anchored tosaid bearing stud (38), and the other, in said cursor (27), and thatsaid bearing stud (38) and said retainer bolt (44) are rotatably mountedin friction bearings (41, 46) pressfitted into said through-bore (37),so that the head (45) of said retainer bolt (44). is at least flush withthe one end of said cursor (27), and said tensioning arm (29) is incontact with the wheel-side end of said cursor (27) or disposedimmediately adjacent thereto.
 8. An electromechanical bicycle gear shiftmechanism according to claim 1, wherein said housing (18) contains apositioning device for said cursor which is associated to said electriccircuit for the control of said electric motor (M) and disposed inalignment with a positioning element (33) displaceable in unison withsaid carrier, characterized in that said electric circuit is disposed ona base plate (31) secured to a housing side, that said positioningelement (33) is provided with a plurality of scanning locations (48,48a, 48b . . . ) for said positioning device disposed on said base plateat mutual spacings corresponding to those of the gear shift stagesprovided, and that said positioning device comprises at least oneopto-electronic sensor (34m) cooperating with said positioning element(33) in a non-contacting manner.
 9. An electromechanical bicycle gearshift mechanism according to claim 8, characterized in that in additionto said scanning locations (38a, 38b . . . ) there are provided twoscanning locations (49, 50) associated to the limit gear shift stages(15a) cooperating, preferably in trailing relationship, with two sensors(34, 34a) for reversing the direction of rotation of said electric motor(M).
 10. An electromechanical bicycle gear shift mechanism according toclaim 9, characterized in that said electric circuit is connectedthrough a logic switch member (60, 61) to a movement or speed sensor(78, 79) from being energized when said chain is at a standstill.
 11. Anelectromechanical bicycle gear shift mechanism according to claim 10,characterized in that said movement or speedsensor (78, 79) for saidchain (9) cooperates with a speed or movement sensor (78, 79) for saidwheel (4) and said logic switch member (60, 61) to form a shift stopcircuit (77) operable in the stationary condition to automaticallyenergize said electric motor (M) for selecting a gear shift stage with asmall transmission ratio or the limit gear shift stage with the smallesttransmission ratio.
 12. An electromechanical bicycle gear shiftmechanism according to claim 8, characterized in that said positioningelement (33) comprises a strip having a row of through-openings andfront and rear switch edges (49, 50), and that said positioning devicecomprises three bifurcate light barriers (34, 34m, 34a) to be actuatedby said strip.
 13. An electromechanical bicycle gear shift mechanismaccording to claim 8, characterized in that each limit bifurcate lightbarrier (34, 34a) is spaced from said bifurcate light barrier (34m) by adistance which is greater by a length (a) than the distance between arespective through-opening (38, 38a) for a limit gear shift stage andthe scanning edge (49, 50) adjacent the respective through-opening, andthat each limit bifurcate light barrier (34, 34a) is connected to arespective circuit section operable to reverse the direction of rotationof said electric motor (M). pg,24